为什么 PagedResourceAssembler 会清除我的模型链接？ [春天 HATEOAS]

问题描述

我想用 Spring Boot 实现 HATEOAS。我实现了它，现在我有另一个分页问题。我只想说分页是这样工作的：

{
  "links": [
    {
      "rel": "first","href": "http://localhost:8080/api/posts?bookId=1&page=0&size=2"
    },{
      "rel": "self",{
      "rel": "next","href": "http://localhost:8080/api/posts?bookId=1&page=1&size=2"
    },{
      "rel": "last","href": "http://localhost:8080/api/posts?bookId=1&page=1&size=2"
    }
  ],"content": [
    {
      "id": 1,"bookId": 1,"title": "UpdatedPost1Title","content": "UpdatedPost1Content","created": "2021-01-18T20:42:39","updated": "2021-01-18T23:16:48","voteUp": 0,"voteDown": 0,"links": [
        
      ]
    },{
      "id": 2,"title": "title2","content": "content2","created": "2021-01-18T20:42:43","updated": "2021-01-18T20:42:43","links": [
        
      ]
    }
  ],

但是正如你所看到的，我所有的内部“链接”都是空的。我运行了调试器，导致这种奇怪行为的行是：

PagedModel<EntityModel<PostDto>> page = pagedResourcesAssembler.toModel(postPage);

从这个方法：

@GetMapping
    @ResponseStatus(HttpStatus.OK)
    public ResponseEntity<PagedModel<EntityModel<PostDto>>> getPosts(@RequestParam(required = false) Long bookId,@PageableDefault(size = DEFAULT_PAGE_SIZE) Pageable pageable) {
        Optional<Long> bookParam = Optional.ofNullable(bookId);

        Page<PostDto> postPage = bookParam.map(aLong -> postService.getByBookId(aLong,pageable).map(assembler::toModel))
                .orElseGet(() -> postService.getAllPosts(pageable).map(assembler::toModel));

        PagedModel<EntityModel<PostDto>> page = pagedResourcesAssembler.toModel(postPage); //this line

        return new ResponseEntity<>(page,HttpStatus.OK);
    }

在此行之前，页面保留有关我之前添加的内部链接的信息 (assembler::toModel)。

我应该怎么做才能防止我的模型被 pagedResourcesAssembler 清除？ （它是 org.springframework.data.web.PagedResourcesAssembler）。

先谢谢你！

解决方法

是的，我在这里找到了答案：https://howtodoinjava.com/spring5/hateoas/pagination-links/。它应该是这样的：

@GetMapping
    @ResponseStatus(HttpStatus.OK)
    public ResponseEntity<PagedModel<PostDto>> getPosts(@RequestParam(required = false) Long bookId,@PageableDefault(size = DEFAULT_PAGE_SIZE) Pageable pageable) {
        Optional<Long> bookParam = Optional.ofNullable(bookId);

        Page<Post> postPage = bookParam.map(aLong -> postService.getByBookId(aLong,pageable))
                .orElseGet(() -> postService.getAllPosts(pageable));

        PagedModel<PostDto> page = pagedResourcesAssembler.toModel(postPage,assembler);

        return new ResponseEntity<>(page,HttpStatus.OK);
    }

如您所见，PagedResourcesAssembler 应该是实体类型，而不是模型类型。我还在创建 PagedModel 之前删除了映射并使用 .toModel(Page,RepresentationModelAssembler) 方法。